Genotype vs Phenotype

Genotype vs Phenotype, what’s the difference and how do I remember which is which?

Genotype is the set of genes an organism carries in its cells.

Phenotype is an organism’s observable or expressed characteristics.

A great way to remember how to distinguish between them is to look at the beginning letters of the words and associate them with a main attribute.

Genotype refers to genes.

Phenotype refers to physical attributes.

Of course, there is much more to genotypes and phenotypes than that so let’s break it down a little more.

Basic Definitions

First, we will need some basic definitions so that we fully understand the similarities and differences of genotype vs phenotype.

DNA: Stands for deoxyribonucleic acid and is a molecule that carries the genetic instructions for all living organisms. Or as we all learned in school “the code of life.”

Gene: A sequence of DNA which codes for a trait.

Example: You have a gene for brown eyes.

Alleles: A variant form of a gene. These are alternate forms of a gene that are obtained from your parents and contain instructions for a trait.

Example: You have one allele for blue eyes from mom and one allele for brown eyes from dad.

Genotype: The genetic makeup of a cell for existing traits that refers to a combination of two alleles.

Example: You have the genotype for being very susceptible to a particular disease.

Phenotype: A trait that is observed or expressed and is influenced by genotype and outside environmental factors. Can also include behaviors as well as physical characteristics.

Example: You have the phenotype for brown hair, or birds have the behavioral phenotype of building nests.

Genotype vs Phenotype Examples

It can be a little tricky to differentiate between genotype vs phenotype because a genotype can also be a phenotype.

A genotype depends on hereditary information (determined by your parents), and it is not influenced in any way by environmental factors.

However, a phenotype depends on genotypes and the influence of environmental factors. To better understand the difference let’s look at some standard examples:

Eye color

This is probably the most classic example you remember from Science class. It’s a genotype and a phenotype.

It’s a genotype because you inherit it from your parents, so you have no control over it. Your parents both have brown eyes? Congrats you will have brown eyes as well.

Brown eyes genotype and phenotype

It’s a phenotype because it is expressed. You can see that your eye color is brown. Functions that are genetic but cannot be seen such as the trait for heart disease would be genotypes only.


Flamingos are another great example. Contrary to popular belief flamingos are not genetically pink. Flamingos are actually born with grey feathers.

The feathers turn pink later on because their diets consist of brine shrimp which contain a natural pink dye called canthaxanthin. This is why you sometimes see non-pink flamingos.

The color pink would be a phenotype since it is not genetically inherited and is the result of outside influences (their diet). The grey color would be a genotype that was predetermined genetically and had no outside influence.

Identical Twins

Identical twins are another example of genotype vs phenotype. Identical twins come from a single fertilized egg that has split into two. They would have the same genotypes such as hair color and predisposition to heart disease. But they could have different phenotypes.

For example, their fingerprints would be different. It would not matter if you started out with the same genes because fingerprints are formed from outside influences such as the temperature of the womb and position of the fetus.

Genotype vs Phenotype In Depth

So now that you are feeling confident with the basics let’s delve into genotype vs phenotype more in-depth.

Our genes have two versions of alleles: dominant and recessive.

They are represented respectively by capital letters (dominant) and lower case (recessive).

This should be dredging up recollections of Science class where you had to a do a ton of Punnett squares.

For example, for hair color, we could use H for dominant and h for recessive.

There are three different types of genotypes. These three genotypes are then expressed as two distinct phenotypes. The three genotypes are as follows:

Homozygous dominant – Where you have two of the same dominant alleles: HH

Homozygous recessive – Where you have two of the same recessive alleles: hh

Heterozygous – Where you have one dominant allele and one recessive allele: Hh

If we continue with our example of hair color, we can say that H represents brown hair color (a dominant trait), and h represents blonde hair color (a recessive trait).

The dominant trait always suppresses the recessive trait.

So this means that HH would be brown hair.

And hh would be blonde hair.

Lastly, Hh would be brown hair.

Even though we have three genotype options (HH, hh, and Hh), they are only expressed as phenotypes in two ways, brown and blonde.

Pretty simple right? Now let’s blow your mind and talk about codominance.

Some genes have alleles that are equal in strength to one another; meaning there is no dominant and recessive. When this happens, it creates an extra trait.

For our example let’s look at flowers. There are three flower color alleles: red, white, and purple.

The allele for red is dominant (R).

Purple is recessive (p).

But white is also dominant (W).

So if you cross a red and a purple flower (Rp) you clearly get a red flower.

But what happens when you cross a red and white flower (RW)?

They are codominant, so they express themselves as an entirely new trait, pink (RW).

Final Thoughts on Genotype vs Phenotype

While genotype vs phenotype can be very confusing initially if you just consider it as gene vs physical, it is much easier to keep track of.

Also, the examples here are very standard, and in real life, there are a multitude of combinations/mutations to take into consideration. You can always delve further into the science behind them, but at the end of the day, the key point to keep in mind is that genotypes are inherited genetically, and phenotypes are expressed or observed.


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